The present invention relates generally to electronic devices having at least an organic active material and, in particular, to such devices having at least a compound electrode.
Efficient operation of electronic devices depends, among other things, efficient transport of charges across an interface between an electrode and an adjacent medium. Opto-electronic devices comprise a class of electronic devices and are currently used in several applications that incorporate the principle of conversion between optical energy and electrical energy. Electroluminescent (“EL”) devices, which are one type of such devices, may be classified as either organic or inorganic and are well known in graphic display and imaging art. EL devices have been produced in different shapes for many applications. Inorganic EL devices, however, typically suffer from a required high activation voltage and low brightness. On the other hand, organic EL devices (“OELDs”), which have been developed more recently, offer the benefits of lower activation voltage and higher brightness in addition to simple manufacture, and, thus, the promise of more widespread applications.
An OELD is typically a thin film structure formed on a substrate such as glass or transparent plastic. A light-emitting layer of an organic EL material and optional adjacent organic semiconductor layers are sandwiched between a cathode and an anode. The organic semiconductor layers may be either hole (positive charge)-injecting or electron (negative charge)-injecting layers and also comprise organic materials. The material for the light-emitting layer may be selected from many organic EL materials that emit light having different wavelengths. The light-emitting organic layer may itself consist of multiple sublayers, each comprising a different organic EL material. State-of-the-art organic EL materials can emit electromagnetic (“EM”) radiation having narrow ranges of wavelengths in the visible spectrum. Unless specifically stated, the terms “EM radiation” and “light” are used interchangeably in this disclosure to mean generally radiation having wavelengths in the range from ultraviolet (“UV”) to mid-infrared (“mid-IR”) or, in other words, wavelengths in the range from about 300 nm to about 10 micrometers.
Reducing or eliminating barriers for charge injection at the organic EL layer/electrode interfaces contributes greatly to enhance the device efficiency. Metals having low work functions, such as the alkali and alkaline-earth metals, are often used in a cathode material to promote electron injection. However, these metals are susceptible to degradation upon exposure to the environment. Therefore, devices using these metals as cathode materials require rigorous encapsulation. In addition, these metals can diffuse rapidly into an adjacent organic EL layer, leading to device performance decay.
Other opto-electronic devices, such as photovoltaic cells, can also benefit from a lower barrier for electron transport across the interface between an active layer and an adjacent cathode.
Therefore, it is desirable to provide cathode materials that efficiently allow electrons to move across an interface between the cathode and an adjacent material and, at the same time, substantially preserve the long-term stability of the device.